This invention relates to an injection moulding process for making articles out of two injectable components, particularly being respectively a plastics material and an elastomeric polymer material. In particular the invention relates to an injection moulding process for making toothbrush bodies, in which a first component is a plastics material and a second component is an elastomeric polymer.
The invention also relates to a toothbrush made using the process of the invention and to moulds and machines for carrying out the process.
Toothbrush bodies, i.e. comprising a grip handle and a head with generally a neck part between all arranged along a longitudinal toothbrush axis, which are made of two components being a hard plastic and a softer elastomer, are known e.g. from EP 0336641A, WO 92/17092 WO 92/17093, and U.S. Pat. No. 5,054,154 among others. Often in such toothbrushes the elastomer is present in two or more places on the toothbrush body, e.g. on the grip handle to enhance grip, and in the neck region to modify flexibility. The elastomer may also be present in other places for decoration.
Usually such toothbrushes are made by firstly moulding the plastic parts of the toothbrush then injecting in the fluid elastomer under conditions which cause the plastic and elastomer to bond. Often when the elastomer is present in two or more places on the toothbrush body these places are linked by a moulding channel so that injection of fluid elastomer at only one injection point into the pre-formed plastic parts of the body, and the fluid elastomer is able to flow along the moulding channels from one part to another. When the elastomer is present in numerous parts separated from one another the presence of a corresponding number of moulding channels to link them is an untidy solution and can lead to weakness of the structure. A self-evident alternative solution to the problem is disclosed in WO 94/05183 in which a number of separate injection points corresponding to the number of places where the elastomer is to be present is used. If the elastomer is present in numerous separated places this can lead to a complex arrangement of injection channels, with consequent difficulty and complexity in making the moulds and ancillary injection moulding machinery.
A further problem is encountered in that if the toothbrush is to have a bulky handle, e.g. in the shape of a character such as an animal, as used for children""s toothbrushes, the bulk also assisting a child""s small hand to grip the handle, a large amount of moulding plastic may be necessary. This adds to weight, cost and use of excessive quantities of materials.
It is an object of this invention to provide an alternative injection moulding process which in part at least overcomes these problems. Other objects and advantages of the invention will be apparent from the following account.
According to this invention a process for making a moulded article comprises the steps of:
in a first mould cavity, having a first internal core within the cavity and distanced from the inner wall surface of the cavity, and having one or more members which extend between the said inner wall and the core, forming by injection moulding of a plastics material a body part having an internal body cavity corresponding substantially to the shape of the first core and having apertures passing through the body from the said body cavity to the outer surface of the body corresponding substantially to the shape and position of the member(s);
separating the formed body from the first mould cavity and removing the first core from the body cavity;
enclosing the formed body in a second mould cavity, and inserting a second internal core into the body cavity, between the second core and the inner surface of the body cavity there being one or more channels in communication with the said apertures when the second core is in place in the body cavity;
injecting a fluid mouldable settable material into the said channels such that the material flows along the channels and into the apertures and then sets;
separating the so-formed article from the second mould cavity and the second core from the body cavity.
Preferred embodiments of the process of the invention will now be described.
The moulded article made by the process is preferably a toothbrush body, i.e. comprising a grip handle and a head with generally a neck part between all arranged along a longitudinal toothbrush axis, with the body cavity within the grip handle. The process of the invention enables the handle to be made bulky but hollow and therefore light in weight. The grip handle may for example be in an attractive shape such as the shape of a character such as a representation of an animal character or cartoon character, so that the toothbrush handle is attractive to children, and preferably to adults as well.
When the moulded article is a toothbrush body as defined above the grip handle is generally a structure elongated along the direction of the toothbrush axis. In this case the body cavity is suitably also an elongate cavity generally following the elongate shape of the body, and the internal cores will consequently be structures elongated along the direction of the toothbrush axis.
The first and second mould cavities are defined in first and second injection moulds which can be provided by known technologies. Injection moulds for toothbrushes, whether pilot or production moulds, the process of the invention being suitable for both, comprise parts, usually two mating halves, made of machined hardened metal, usually steel, which must fit together with great precision and which when fitted together enclose an accurately dimensioned internal cavity which defines the shape of the final toothbrush product, and into which is injected the material of the toothbrush. The crucial part of such moulds are their internal cavity, the features of which are dictated by the function of defining the shape of the final toothbrush product. The mould cavities within such moulds are normally formed by a process of spark erosion otherwise known as electrical discharge machining, which is for example practiced by such European toothbrush mould manufacturers as Anton Zahoransky GmbH (DE) and Machines Boucherie NV (BE). Such moulds also necessarily incorporate ancillary operative and constructional features, for example a mould frame, e.g. comprising injection points for plastic and elastomer materials, to enable the mould to match a standard injection moulding machine as used by a toothbrush manufacturer.
The first mould cavity and the second mould cavity are preferably made in a multi-part, e.g. two-part mould construction, each part defining a respective part of the mould cavity thereby allowing the mould cavity to be opened to allow the body to be separated from the mould. Moulds of this general type, of multi-part construction, for use in injection moulding processes for the manufacture of toothbrushes and similar moulded articles, and in which the article is formed by injection moulding into a mould cavity within the mould are well known in the art. Typically each part of such a two-part mould may comprise a block of the metal having cut into it a part mould cavity, and when the two blocks are put together the two part cavities define the entire mould cavity.
Toothbrush moulds generally are of such two part construction, each part defining a part mould cavity which corresponds to the entire mould cavity split generally along the toothbrush axis. In such a mould the first and second mould cavities may have an open end at the end remote from the toothbrush head, and through which the mould cores may extend. In such a construction the mould cores may taper along the length of the toothbrush grip handle, being wider at the end remotest from the toothbrush head. This enables the mould core to be easily withdrawn from the body cavity.
The one or more members are preferably located on the inner wall surface of the first mould cavity, and are preferably made integrally with the mould, enabling the members to be easily removed from the formed apertures, for example as the mould is opened. Alternative constructions are possible, for example members may project from or be made integrally with the first core. The apertures, and correspondingly the members, may taper, narrowing in dimension from their outer end toward their inner end, again facilitating separation. When the apertures are filled with the second material their open outer ends form areas of the second material exposed and visible on the outer surface of the body of the article.
Between the inner wall of the second mould cavity and the body there may be convexities, e.g hollows in communication with the said apertures and channels, allowing the second material to flow into these convexities and form areas of second material exposed at the surface of the formed article. These areas of exposed second material can enhance the appearance of the article and, particularly if they are convex bulges, can enhance grip. In the type of childrens"" toothbrush mentioned above, the areas may for example form features of the character. Alternatively the areas of exposed second material, or contrasting first material within such areas, may spell out and display textual matter such as a trade mark used in relation to the product. Such display techniques are well known in the toothbrush art.
Suitably the respective plastic material and elastomer are known materials used in two-component toothbrush manufacture and may be of contrasting or complementary colours to emphasise the construction of the article such as a toothbrush by producing a visual effect. For example if the grip handle is in the form of an animal character exposed areas of the elastomer may represent features of the character e.g. coloured patches or stripes. Injection moulding conditions for such materials are well known.
In an optional further step of the process of the invention when the second core has been removed from the body cavity the body cavity may be closed by a closure, such as a plug or cap that may be fitted into the open end of the body cavity by conventional means such as a snap-fit or friction fit etc. This closure may be shaped to further enhance the visual appearance of the article, e.g. in the case of a character-shaped children""s toothbrush being in the form of feet for the character. Alternatively the closure may be visually relatively insignificant. In the case of articles which are bulky handled toothbrushes the closure or the body itself may have a flat end perpendicular to the axis of the toothbrush, or a sucker etc. enabling the toothbrush to be stood upright thereupon.
The process of the invention may be automated, for example to enable mass-production of products such as toothbrushes. Suitable injection moulding machines capable of using moulds of the kind described above and the process of the invention are commercially available, e.g. from the abovementioned Anton Zahoransky GmbH and Machines Boucherie NV.
When a toothbrush body is made by the above described moulding process, the moulding process may be followed by a subsequent process of providing the toothbrush with bristles. These may be provided by known bristle introduction processes. For example the toothbrush head may be moulded with socket holes into which the bristles may subsequently be inserted in a well known process. Alternatively the bristles may be moulded into the head material, e.g. by an application of known processes such as that disclosed in EP 0293665 or WO 95/30350. Alternatively the toothbrush head and handle may be formed separately, e.g. by the process described in PCT/EP 96/02978 the content of which is included herein by way of reference.
The invention also provides a first mould cavity adapted for use in the process of this invention.
The invention also provides a first mould adapted for use in the process of this invention, for example incorporating a first mould cavity as described above.
The invention also provides a first internal core for use in the process of this invention.
The invention also provides a second mould cavity adapted for use in the process of this invention.
The invention also provides a second mould adapted for use in the process of this invention, for example incorporating a second mould cavity as described above.
The invention also provides a second internal core adapted for use in the process of this invention.
The invention also provides a process in which such above-mentioned moulds and cavities are made, for example a spark-erosion or electrical discharge machining process.
The invention also provides a moulded article, particularly a toothbrush body, made by the process of this invention.
Such a toothbrush for example comprises a bristle-bearing head and a hollow moulded grip handle body having a body wall made of plastics material, having apertures passing through its plastics material body wall from an internal body cavity to the outer surface, the apertures being filled with a moulded second material, the second material in the cavities being linked by residual second material in moulding channels in, or residual second material on the inner surface of the body cavity. The internal body cavity of the toothbrush may be closed by a closure at its end remote from its head.
The so formed toothbrush may incorporate known features such as a handle which includes a folded region as disclosed in EP 0336641A or by using the process of this invention or otherwise, cut-outs, e.g. as described in U.S. Pat No. 5,054,154, filled with elastomeric material may be incorporated into the handle, neck or head to modify flexibility.